This invention relates to an exhaust silencer unit for a marine propulsion unit and more particularly to an improved expansion chamber type of silencing device for the exhaust gases of a marine propulsion unit.
It is well known that the exhaust gases of internal combustion engines can, if emitted to the atmosphere unmuffled, create substantial noise. It has, therefore, been the practice to provide some form of silencing device in the exhaust system for such engines. The problems of silencing the exhaust gases of an internal combustion engine are magnified when the engine runs over a wide range of speeds and load conditions since the tuning of the exhaust system for these varying conditions can give rise to substantial problems. In addition, when the exhaust system is used in a marine vehicle, still further problems are encountered because of the relatively small space and confined area in which the exhaust system maybe provided.
It is, therefore, a principal object of this invention to provide an improved exhaust silencer for the exhaust gases of an internal combustion engine.
It is a further object of this invention to provide a high efficiency, relatively small size exhaust silencer for a marine propulsion unit.
It is a still further object of this invention to provide an improved exhaust silencer unit for a marine propulsion unit that has a compact configuration and yet which provides good silencing under a wide range of engine running conditions.
The use of expansion chambers in exhaust systems is well known to achieve good silencing. The expansion chamber is effective to produce the good silencing under a wide range of load conditions and the number of expansion chambers employed in the exhaust system can significantly improve the silencing. However, in connection with marine propulsion units it has been difficult to provide plural expansion chambers due to the relatively small size in compact nature required for the exhaust system.
In addition, it is well known in marine propulsion units to mix the coolant from the engine cooling system with the exhaust gases and discharge them together. This provides a simplicity in the plumbing arrangement for the engine and also the addition of the cooling water to the exhaust gases can improve silencing. However, it must be ensured that the coolant from the engine cooling jacket and also the water from the body of water in which the watercraft is operating does not re-enter the engine through the exhaust system which could cause damage to the engine.
It is, therefore, a further object of this invention to provide an exhaust system for a marine propulsion unit embodying multiple expansion chambers and which ensures that water cannot re-enter the engine through exhaust ports.